This invention relates to a high nitrile content based resin and more particularly to a polymer composite with high impact resistance, excellent processibility, excellent gas barrier property and chemical resistance.
In graft polymerizing ethylenical unsaturated nitrile in the presence of a rubber component, the proportion of ethylenic unsaturated nitrile is lower in the first step polymerization product than in the final polymerization product and is higher in the second polymerization product than in the final polymerization product so that the composite is substantially heterogeneous.
The so-called nitrile based resin having a relatively high content of unsaturated nitrile excels in gas barriering property and chemical resistance. Thus, such resin has been used as packaging material and as other industrial material. A copolymer made from acrylonitrile and aromatic vinyl compound is not thermally deformable even at a relatively high temperature. Thus, when it is strengthened with rubber, in particular, its usefullness increases. However, the polymerizability is so widely apart between acrylonitrile and aromatic vinyl compound that when the conventional radical polymerization process is carried out, the compositions produced at an earlier polymerization stage show a considerable difference from the compositions produced at a later polymerization stage As a result, the final product tends to be heterogeneous with lower impact resistance and lower thermal stability.
To be more specific, in conventional radical polymerization process, the highly reactive aromatic vinyl compound is apt to polymerize at an earlier stage to give a copolymer which contains the aromatic vinyl compound richer than the starting material contains, whereas the less reactive acrylonitrile polymerizes at a later stage to give a copolymer which contains a large amount of the acrylonitrile. For this reason, various proposals have been put forth in the art for producing a homogeneous copolymer or for strengthening a copolymer with rubber.
Among the proposed processes, for example, is Japanese Patent Publication No. 33574/1971 which discloses a method wherein an aromatic vinyl compound is added to acrylonitrile steadily in the presence of diene based rubber so as to keep constant the refluxing temperature. Japanese Patent Publication No. 16347/1973 discloses a method wherein monomers composition are gas chromatographically traced in the reaction system and monomers are added to maintain a constant composition, thereby to produce a copolymer with homogeneous composition. However, disadvantageously such a method does not produce a very high yield. In Japanese Patent Publication No. 1950/1974, there is disclosed a method wherein a reactive compound is added to the polymerization system according to the degree of heat evolved.
All of the foregoing proposals have in common alleged production of a uniform copolymer by preliminarily preparing a certain composition of monomer mixture in order that a copolymer may be obtained in the predetermined composition, and while tracing the reaction progress, adding a part of the monomer mixture to the reaction system so as to retain the initial composition. Nevertheless, in these proposals, there have been and are many unresolved problems, such as, the heat evolved during polymerization can hardly be removed on account of the initial amount of monomers put in a reactor being too plentiful. However, the reaction progress has to be continuously monitored. The monomers must be added with great care according to the progress of the reaction. Furthermore, the operation and equipment employed must be complicated to obtain a uniform copolymer. In addition to these deficiencies and difficulties, and regardless of the uniformity of the obtained copolymer, the fluidity of the produced copolymer is substantially deficient.